We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

What is Thermoplastic Injection Molding?

By Harris Maryland
Updated: May 17, 2024

Thermoplastic injection molding is a process used in manufacturing to create a variety of parts and components for industries ranging from aerospace to automotive to construction. Thermoplastics, such as phenolic and epoxy, are heated into a molten resin and then injected into a mold that’s usually made from aluminum, steel or a metal alloy. The molten plastic then gets compressed inside the mold and allowed to cool. Machines remove the plastic component or piece from the mold, and this hardened part can then be used to construct a larger product, such as a child’s toy or an automobile door.

The thermoplastic injection molding industry churns out literally thousands of products and supports hundreds of industries. As of the 1990s, nearly 20,000 different types of thermosetting and thermoplastic materials were used for injection molding. Industrialists commonly use dyes and other agents to alter the properties of the molten plastic resin, such as its color, hardness, and springiness. The molds used to shape the molten plastic generally must be precut in a separate process, using sophisticated tooling procedures to properly prepare them. A device called a sprue allows the molten resin to enter the mold and fill up the cavity. Molds also are typically designed to allow air bubbles to escape. Otherwise, during compression and heating, the air bubbles might deform the plastic and even create internal burning of the finished components.

Pre-hardened steel molds tend to be more expensive but may be longer lasting; thus, manufacturers often use these harder, higher-quality steel molds for high-volume thermoplastic injection molding jobs. For more boutique industrial work, manufacturers may use aluminum molds, which can be more cost effective for scaled-down operations. To tool molds for industrial plastic injection work, manufacturers typically employ one of two time-tested processes: electrical discharge or standard machining. With the electrical discharge process, a robot applies a voltage from a tool to alter the shape of the base metal. With standard machining, a more conventional process, a machine or tool physically warps the mold into its final shape.

Manufacturers can experiment with literally dozens if not hundreds of variations in the thermoplastic injection molding process to optimize their processes. Changes can be made to the pressure applied to the mold, the speed of the injection of the resin plastic or to the geometry and structure of the molds. Other alterations may include the cooling time of the plastic, the pressure in the cavity, the composition of the dye, and the variety of plastic resin additives.

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.